The invention relates in general to digital image recording and printing in an apparatus including an ink jet device for forming an ink image on a member. In particular, a coagulable ink is used in the ink jet device, coagulates are formed in the ink image on the member, excess liquid is removed from the coagulates while the coagulates remain on the member, and the coagulates are subsequently transferred to a receiver.
High resolution digital input imaging processes are desirable for superior quality printing applications, especially high quality color printing applications. As is well known, such processes may include electrostatographic processes using small-particle dry toners, e.g., having particle diameters less than about 7 micrometers, electrostatographic processes using nonaqueous liquid developers (also known as liquid toners) in which particle size is typically of the order of 0.1 micrometer or less, and ink jet processes using aqueous-based or nonaqueous inks. The less commonly used nonaqueous ink jet technology has an advantage over aqueous-based ink jet technology in that an image formed on a receiver requires relatively little drying energy and therefore dries relatively rapidly.
The most widely used high resolution digital commercial electrostatographic processes involve electrophotography. Although capable of high process speeds and excellent quality printing, electrophotographic processes utilizing dry or liquid toners are inherently complicated, and require expensive, bulky and complex equipment. Moreover, due to their complex nature, electrophotographic processes and electrophotographic machines tend to require significant maintenance.
Digital ink jet processes have the inherent potential to be simpler, less costly, and more reliable than digital electrophotographic processes. Generally, it is usual for ink to be fed through a nozzle, the diameter of which nozzle being a major factor in determining the droplet size and hence the image resolution on a recording surface. There are two major classes of ink jet printing, namely, continuous ink jet printing and drop-on-demand ink jet printing. Continuous printing utilizes the nozzle to produce a continuous stream of electrically charged droplets, some of which droplets are selectively delivered to the recording surface, the remainder being electrostatically deflected and collected in a sump for reuse. Drop-on-demand ink jet printing produces drops from a small nozzle only as required to generate an image, the drops being produced and ejected from the nozzle by local pressure or temperature changes in the liquid in the immediate vicinity of the nozzle, e.g., using a piezoelectric device, an acoustic device or a thermal process controlled in accordance with digital data signals. In order to produce a gray scale image, variable numbers of drops are delivered to each imaging pixel. Typically, an ink jet head of an ink jet device includes a plurality of nozzles. In most commercial ink jet systems, aqueous-based inks containing dye colorants in relatively low concentrations are used. As a result, high image densities are difficult to achieve, image drying is not trivial, and images are not archival because many dyes are disadvantageously subject to fading. Moreover, the quality of an aqueous-based ink jet image is strongly dependent upon the properties of the recording surface, and will for example be quite different on a porous paper surface than on a smooth plastic receiver surface. By contrast, the quality of an electrophotographic toner image is relatively insensitive to the recording surface, and the toner colorants in both dry and liquid electrophotographic developers are generally finely divided or comminuted pigments that are stable against fading and able to give high image densities.
To overcome problems associated with fading and low image densities associated with dyed aqueous-based inks, pigmented aqueous-based inks have been disclosed in which a pigmented material is colloidally dispersed. Typically, a relatively high concentration of pigmented material is required to produce the desired highest image densities (Dmax). Exemplary art pertaining to pigmented aqueous-based inks includes the recently issued Lin et al. patent (U.S. Pat. No. 6,143,807) and the Erdtmann et al. patent (U.S. Pat. No. 6,153,000). Generally, pigmented inks have a much greater propensity to clog or modify the opening jet(s) of a drop-on-demand type of ink jet head than do dyed inks, especially for the narrow diameter jets required for high resolution drop-on-demand ink jet imaging, e.g., at 600 dots per inch. Drop-on-demand printers do not have a continuous high pressure in the nozzle, and modification of the nozzle behavior by deposition of pigment particles is strongly dependent on local conditions in the nozzle. In continuous ink jet printers using pigmented inks, the relatively high concentrations of pigment typically affects the droplet breakup which tends to result in nonuniform printing.
Pigmented nonaqueous inks having particle sizes smaller than 0.1 micrometer for use in ink jet apparatus are disclosed in the Romano et al. patent (U.S. Pat. No. 6,053,438), and the Santilli et al. patent (U.S. Pat. No. 6,166,105).
Long term stability (good shelf life) is an important property of both aqueous-based and nonaqueous colloidal dispersions useful for commercial ink jet inks. The principles of stabilization and destabilization are well documented for aqueous-based and nonaqueous colloids, such as for example in articles by B. J. Carroll in Surface and Colloid Science, Volume 9, pp 1-68, (Wiley, 1976), by J. Th. G. Overbeek in Colloidal Dispersions, Special Publication No. 43, pp 1-22, (The Royal Society of Chemistry, 1982), and D. H. Napper, ibid., pp 99-128, and in the book by D. H. Everett, Basic Principles of Colloid Science, (The Royal Society of Chemistry, 1988). To prevent attractive dispersion forces (or Van der Waals forces) from producing flocculation and coagulation of colloidally dispersed particles, aqueous-based dispersions are typically electrostatically stabilized by electrostatic repulsions between the electrical double layers surrounding charged colloidal particles, and nonaqueous dispersions are typically sterically stabilized. A degree of steric stabilization can be important for certain aqueous-based colloids which are primarily electrostatically stabilized. Similarly, a degree of electrostatic stabilization can be important for certain nonaqueous colloids which are primarily sterically stabilized, such as for example a typical electrographic liquid developer. As described in the references cited above in this paragraph, electrostatically stabilized liquid dispersions may be destabilized by the addition of ionic salts, by changing the pH, by application of an electric field, and by heating or cooling. Sterically stabilized liquid dispersions may be destabilized by heating or cooling, by application of an electric field, by adding a non-solvent for the solution-embedded ends of sterically stabilizing polymeric moieties adsorbed to the colloid particle surfaces (i.e., adding a non xcex8-solvent), or by adding an excess of stabilizing polymer. It is accepted usage to refer to flocs as precursors to coagulates, the flocs generally being loosely or reversibly bound, and the coagulates irreversibly bound. Hereinbelow, both flocs and coagulates may be referred to as aggregates or agglomerates.
A deficiency associated with most high resolution conventional ink jet devices that deposit ink directly on to a (porous) paper receiver sheet is an unavoidable tendency for image spreading, with a concomitant resulting degradation of resolution and sharpness of the image produced. As a drop of deposited liquid ink is absorbed, capillary forces tend to draw the ink along the surface and into the microchannels between paper fibers, thereby causing a loss of resolution. Inasmuch as the colorant concentration of a dyed aqueous-based ink tends to be low, there is a comparatively large proportion of liquid vehicle which must be absorbed from each drop. This also holds true for the case of pigmented aqueous-based inks, for which particle sizes may be sub-micron, i.e., such very small particles can be swept along by the carrier liquid as it spreads in the paper, thereby compromising high resolution imaging quality. In addition to capillary spreading by liquid absorption in a receiver, spreading may also be a problem if the carrier liquid is not readily absorbed by a receiver, e.g., if the receiver is a coated specialty paper used in a high resolution conventional ink jet device that deposits ink directly on to a receiver. The spreading is strongly dependent upon the surface energies of the coating on the paper and of the ink. Unusual particle size distributions such as disclosed in the above-cited Lin et al. patent (U.S. Pat. No. 6,143,807) may be useful with pigmented aqueous-based inks, perhaps to mitigate the effects of image spread.
A way to control image spread of an ink jet image is to cause a precipitation, coagulation, agglomeration or aggregation of an ink jet ink colorant near the surface of a porous receiver. In particular, such a technique is useful for aqueous-based dyed ink jet inks. The Tsuchii et al. patent (U.S. Pat. No. 5,805,190) discloses types and amounts of a xe2x80x9cprint property improving liquidxe2x80x9d ejected by a jetting device on to a location on receiver prior to a colorant ink jetted to the same location. The Shioya et al. patent (U.S. Pat. No. 5,864,350) discloses depositing a liquid for coagulating a dye contained in a colored ink jet ink after a previous colored ink jet ink has been deposited on a receiver. The Yatake patent (U.S. Pat. No. 6,004,389) discloses an ink jet ink composition such that a xe2x80x9creaction solution, containing a reactant, capable of breaking the state of dispersion and/or dissolution of a pigment in the ink composition is brought into contact with the ink compositionxe2x80x9d. The reaction solution may be deposited on a receiver before or after the ink jet ink, either over the entire surface of the receiver or selected portions, e.g., using a jetting device. The reagent solution may include cationic compounds such as inorganic metal salts, primary, secondary and tertiary amines, ammonium and phosphonium compounds. The Inui et al. patent (U.S. Pat. No. 6,062,674) discloses the use of a coagulating liquid to enhance the black image portion of an ink jet image on a receiver. The Shioya patent (U.S. Pat. No. 6,084,621) teaches jetting an xe2x80x9cinvisiblexe2x80x9d latent image on to a receiver, which latent image includes a coagulating agent or chemical, the latent image being developable by a coagulable ink jet ink deposited on the same pixels as the latent image. The Kasamatsu et al. patent (U.S. Pat. No. 6,062,674) discloses use of a xe2x80x9ctreatment liquidxe2x80x9d for aggregating the dye in an ink jet ink on a receiver to prevent penetration of the dyestuff into a receiver, thereby making the image water resistant and improving fade resistance. The Fujita et al. patent (U.S. Pat. No. 6,099,116) discloses that the amount of a xe2x80x9cprocessing liquidxe2x80x9d can be adjusted for each imaging pixel independently to provide an ink jet image on a receiver with sufficient water resistance. The Kato et al. patent (U.S. Pat. No. 6,102,537) discloses a xe2x80x9cprinting property improving liquidxe2x80x9d for creating an improved multicolor ink jet image on a receiver, which xe2x80x9cprinting property improving liquidxe2x80x9d may be applied to selected imaging pixels before, between, or after the jetting of each color ink jet ink. The Tajika et al. patent (U.S. Pat. No. 6,120,141) discloses partial overlapping of places on a receiver where ink jet ink and a xe2x80x9cprintability improving liquidxe2x80x9d are deposited. The Inui et al. patent (U.S. Pat. No. 6,123,411) describes the deposition of a xe2x80x9crecording-improvement liquidxe2x80x9d on pixels at boundaries around groups of imaging pixels to prevent spreading or xe2x80x9cfeatheringxe2x80x9d of an ink jet image on a receiver. The Suzuki et al. patent (U.S. Pat. No. 6,153,001) describes a xe2x80x9cfixing agentxe2x80x9d which may include divalent and trivalent inorganic cations, which xe2x80x9cfixing agentxe2x80x9d is applied to a receiver before or after the arrival of an ink jet ink image on the receiver. The Oikawa patent (U.S. Pat. No. 6,164,773) discloses the ejection of a coagulating xe2x80x9cprinting improvement liquidxe2x80x9d on to a receiver before or after deposition of an ink jet image on the receiver, the apparatus preventing the xe2x80x9cprinting improvement liquidxe2x80x9d from splashing back from the receiver to the ink jet head to cause a clogging of the jets.
An intermediate element or member may be used with an ink jet device in which device one or more colored inks may be deposited via ink jet on to the surface of the intermediate member and subsequently co-transferred to a receiver such as a paper sheet. It is worthy of note that in none of the ink jet imaging patents cited above in the previous paragraph is a coagulation process or reagent used to produce a coagulated image on an intermediate member. In the Anderson patent (U.S. Pat. No. 5,099,256) an intermediate member having a thermally conductive silicone surface that is rough to prevent image spreading is heated to dehydrate an aqueous-based ink jet image formed thereon prior to transfer of the ink jet image to a receiver. The Okamato et al. patent (U.S. Pat. No. 5,598,195) discloses an ink jet recording method, in which a voltage pulse applied to an electrode in an ink jet recording head and an opposing electrode disposed on the opposite side of an intermediate recording material produces a Coulomb force that causes an ink to be jetted on to the intermediate recording material. The Xu patent (U.S. Pat. No. 5,746,816) discloses an aqueous-based liquid ink containing an insoluble dye. Such an ink containing an insoluble dye is used in the Hale et al. patent (U.S. Pat. No. 5,830,263) which discloses a method in which a liquid ink containing a heat activated dye is imagewise deposited via an ink jet device on an intermediate member, which dye being subsequently released and thereby transferred to a receiver sheet by combined heat and pressure. The Hirata et al. patent (U.S. Pat. No. 5,949,464) describes an ink jet ink curable by ultraviolet light for use in conjunction with an intermediate member. The Koike et al. patent (U.S. Pat. No. 5,988,790) discloses an aqueous-based-based ink jet ink for use with an intermediate member in a printer. The Komatsu et al. patent (U.S. Pat. No. 6,059,407) describes the use of a surfactant applied to the surface of an intermediate member employed in an ink jet recording method. The Jeanmaire et al. patent (U.S. Pat. No. 6,109,746) discloses a method of use of an intermediate member in an ink jet machine, which intermediate member includes cells where aqueous-based ink jet drops are mixed to provide a desired color in each cell, the mixed inks subsequently transferred to an image receiver. The Suzuki et al. patent (U.S. Pat. No. 6,153,001) cited in the previous paragraph discloses a pigmented ink including water and an aqueous organic solvent, which ink may be used with an intermediate member in an ink jet recording method.
Ink jet processes employing an intermediate member can use so-called phase change inks. The Titterington et al. patent (U.S. Pat. No. 5,372,852) describes a molten ink which solidifies on contact with a liquid layer on the surface of an intermediate member. Similarly, the Bui et al. patent (U.S. Pat. No. 5,389,958) describes a phase change ink deposited on a sacrificial liquid layer on an intermediate member. The Jones patent (U.S. Pat. No. 5,864,774) discloses a melted ink jetted to an intermediate member. The Urban et al. patent (U.S. Pat. No. 5,974,298) discloses a duplex ink jet apparatus employing phase change ink jet ink on an intermediate transfer surface. The Ochi et al. patent (U.S. Pat. No. 6,102,538) describes a phase change ink jet ink which undergoes a viscosity change when ink droplets arrive at the surface of an intermediate member. The Burr et al. patent (U.S. Pat. No. 6,113,231) describe an offset ink jet color printing method in which hot melt ink droplets harden after deposition on an intermediate member, such that different color inks are overlaid on the intermediate member and subsequently co-transferred to a final receiving medium.
A novel type of electrographic apparatus for depositing drops of nonaqueous liquid inks containing pigmented particles is disclosed in the Newcombe et al. patent (U.S. Pat. No. 5,992,756), the Taylor et al. patent (U.S. Pat. No. 6,019,455), the Lima-Marques patent (European Patent No. 0646044), the Emerton et al. patent (European Patent No. 0760746), the Newcombe et al. patents (European Patent Nos. 0885126 and 0885128), the Janse van Rensburg patent (European Patent No. 0885129), the Mace et al. patent (European Patent No. 0958141), and the Newcombe patent (European Patent No. 0973643). The nonaqueous liquid inks that are used include electrically charged pigmented particles and oppositely charged inverse micelle counterions. Ink is supplied to a writing head wherein the electroscopic pigmented particles are concentrated near an ejection location. By applying controlled voltage pulses, agglomerates or clusters of the pigmented particles are electrostatically ejected from the ejection location and travel to the surface of a receiver member. As a result of agglomeration, relatively little liquid is carried to the receiver, requiring little or no drying or removal of excess liquid from the receiver. Although a physical understanding of how the particles are concentrated has not yet been elucidated in detail, the concentrating of the pigmented particles near the ejection location (accompanied by at least a partial separation from counterions) is attributed to electrophoretic and dielectrophoretic forces. These electrophoretic and dielectrophoretic forces are induced by a number of important factors which may not as yet be optimized, including a suitable geometrical arrangement of electrodes in the writing head, suitable potentials applied to the electrodes, a suitable geometry of the ejection location, and a suitable geometry of the liquid flow channels within the head. This type of novel apparatus tends to have an inherent problem with plateout of particles, at or near the ejection location, thereby deleteriously affecting performance. There is also a problem with replenishment of non-agglomerated ink in the vicinity of a nozzle and removal of the particle-depleted carrier liquid from the vicinity of the nozzle. Another difficulty is a need for a complex writing head including a number of properly disposed electrodes and associated applied potentials. Such apparatus also has a disadvantage by comparison with conventional liquid developer electrophotography in that the associated ink technology is relatively immature. For example, specially tailored inks are needed to provide suitable agglomeration behavior in the write head. Such inks are reported to need high resistivities, higher than the resistivity of a typical electrophotographic liquid developer. Moreover, the inks require a suitable stability or keeping property for practical utility in the marketplace. Long keeping or storage time is a characteristic that was historically difficult to achieve for commercial electrophotographic liquid developers. Nonaqueous liquid inks suitable for use with a writing head of an apparatus of the above disclosures are described in the Nicholls et al. patent (U.S. Pat. No. 5,453,121) and the Nicholls patents (U.S. Pat. No. 6,117,225 and European Patent No. 0939794). Similar apparatus and types of inks are disclosed in the Kohyama patent (U.S. Pat. No. 6,126,274) for image recording, and the Kato patent (U.S. Pat. No. 6,133,341) for making lithographic printing plates. The Nicholls patent (U.S. Pat. No. 6,117,225) cited above discloses an improved ink which reduces plateout, the improved ink including marking particles covered with a highly resistive coating.
The aforementioned Kato patent (U.S. Pat. No. 6,133,341) describes the use of a head for ink jet recording including a narrow electrode mounted in a slit, such that droplets of nonaqueous ink are discharged from the discharge slit upon application of a voltage to the discharge electrode; this patent does not explicitly mention a concentrating of the pigmented particles before droplets are discharged from the head.
The above-cited Kohyama patent (U.S. Pat. No. 6,126,274) discloses the use of an intermediate image receiving member for receiving agglomerated marking particles ejected from the writing head. This intermediate image receiving member is a moving web, and a particulate image formed on this web by the writing head is transported by the web to a transfer nip where the particulate image is transferred to a receiver member. Transfer of the marking particles to the receiver may be effected thermally or electrostatically.
The use of a preferably compliant intermediate transfer member in liquid developer electrophotography is well known, e.g., see recent patents including the Gazit et al. patent (U.S. Pat. No. 5,745,829), the Fujiwara et al. patent (U.S. Pat. No. 5,745,830), the Tarnawskyj et al. patent (U.S. Pat. No. 5,761,595), the Hara et al. patent (U.S. Pat. No. 6,097,920), the Nakano et al. patent (U.S. Pat. No. 6,115,576), and the Miyamoto et al. patent (U.S. Pat. No. 6,146,804). An intermediate transfer member is of particular utility for successively receiving, from one or more photoconductive imaging members, a plurality of single color liquid developer toner images transferred in register with one another to form a plural toner image on the intermediate member, the plural or full color toner image being subsequently transferred from the intermediate member to a receiver member.
As is well known, most electrophotographic liquid developers include only a small percentage by weight of toner solids. Typically, less than about 5% by weight of a liquid developer is toner, the remainder being a carrier liquid or dispersant in which the toner particles are dispersed. The toner particles generally have diameters less than about 3 micrometers, typically 1 micrometer or less. Inasmuch as a toner particle image immediately after transfer to a receiver sheet preferably contains a minimum amount of liquid, various methods have been disclosed to remove excess carrier liquid or developer from a wet electrographic liquid toner image, the wet toner image being located on an imaging member or on an intermediate transfer member prior to removal of excess liquid.
The Landa et al. patent (U.S. Pat. No. 4,286,039) describes removal of excess developer from a photoconductor using a deformable squeegee roller biased to a voltage having a polarity of the same sign as that of the toner particles. The Moraw patent (U.S. Pat. No. 4,482,242) describes removal of excess developer from a photoconductive drum using a stripper roller rotating 20% faster than the drum. The Moe et al. patent (U.S. Pat. No. 5,754,928) and the Teschendorf et al. patents (U.S. Pat. Nos. 5,713,068, 5,781,834 and 5,805,963) describe removal of excess developer liquid using a squeegee roller. The Tagansky et al. patent (U.S. Pat. No. 5,854,960) describe removal of excess liquid from a surface, leaving a portion of the liquid for transfer to another surface. The Kellie et al. patent (U.S. Pat. No. 6,091,918) describes removal of excess developer liquid using a squeegee roller having a core with a crowned profile.
The Asada et al. patent (U.S. Pat. No. 5,765,084) describes use of squeeze rollers to remove excess developer liquid from a photoconductive member and to control the thickness of the developer liquid prior to toner transfer from the photoconductive member to an intermediate member. A full color imaging apparatus is described in which a corona charge having a polarity the same as the polarity of the charge on the toner particles is applied to a first color toner image after transfer of the first color image to the intermediate member. A similar corona charging procedure is followed after a second color toner image has been transferred in registry on top of the first color toner image, and the process repeated until a full color toner image is on the intermediate member for subsequent transfer to a receiver sheet. The corona chargings after each transfer to the intermediate member levels the surface potential and also retards back transfer of toner to the imaging member.
In the Landa et al. patent (U.S. Pat. No. 4,974,027) an apparatus for xe2x80x9crigidizingxe2x80x9d a liquid developed toner image on an image bearing surface prior to transfer is described, including using a squeegee device such as a metering roller to remove excess liquid and applying an electric field between the image bearing surface and another member, e.g., a roller in close propinquity to the image bearing surface. In the Domoto et al. patent (U.S. Pat. No. 5,974,292) an apparatus including liquid development is described for metering post-development fluid laid down on an imaging belt after development of a latent image, wherein a compacting of a toner image on the imaging belt is accomplished by the application of an electric field in a direction to urge the toner particles towards the surface of the imaging belt.
In the Simms et al. patent (U.S. Pat. No. 5,332,642) a device and method are disclosed for increasing the solids content of a liquid-developed image on an absorptive image carrying member such as a primary imaging member or an intermediate transfer member. The image carrying member may be a porous roller provided with an interior vacuum mechanism for drawing carrier fluid through the absorptive material of the roller, the roller also being electrified with a polarity to repel toner particles from the absorptive or porous material so that minimal toner particles are transferred to the absorptive material. In the Moser patent (U.S. Pat. No. 5,723,251) an intermediate transfer member roller is disclosed for liquid development electrophotography which includes an absorptive layer for imbibing carrier liquid from a toner image on the intermediate transfer roller. A contact member may be used for squeezing the imbibed liquid from the intermediate transfer roller. Alternatively, a vacuum may be used for sucking the imbibed liquid from the absorptive layer, or a heating or cooling member may be used for xe2x80x9csweatingxe2x80x9d liquid from the absorptive layer. In the Herman et al. patent (U.S. Pat. No. 5,965,314) an intermediate transfer member is described that contains a material which is capable of absorbing carrier liquid in amounts from 5% to 100% by weight, based on the weight of the absorbing material, after ten minutes of soaking. Suitable absorbing materials are elastomeric materials having an affinity for hydrocarbon carrier liquids, such as crosslinked isoprene, natural rubber, EPDM rubber and certain crosslinked silicone elastomers.
The Landa et al. patent (U.S. Pat. No. 4,286,039) previously cited herein above discloses the use of a blotting roller to absorb excess developer liquid from a photoconductor. The blotting roller is biased by a potential having a sign the same as a sign of the toner particles in the developer, and includes a closed-cell polyurethane foam formed with open surface pores. Devices are provided for squeezing liquid absorbed by the pores from the pores so as to continuously present open dry pores for blotting. The Landa patent (U.S. Pat. No. 4,392,742) similarly describes a blotting roller having externally exposed internally isolated surface cells. The Kurotori et al. patent (U.S. Pat. No. 4,985,733) discloses a blotting roller, a transfer sheet including a liquid developed image facing the blotting roller, and a backup roller behind the transfer sheet. The blotting roller removes excess liquid prior to fusing the image in a fusing station. The Simms et al. patent (U.S. Pat. No. 5,965,314) discloses an absorptive belt to draw off liquid toner carrier liquid from a wet image located on an image carrying member such as an electrostatographic imaging member or intermediate transfer member. The belt is semiconductive and is passed over a roller that is biased to a potential of the same polarity as that of the toner particles. Fluid is removed from the belt by a squeegee roller. The Larson et al. patent (U.S. Pat. No. 5,839,037) discloses a multicolor imaging electrostatographic apparatus including a photoconductive imaging belt passing through a plurality of color stations wherein each color station forms a different color liquid developed toner image on the belt, each successive image being formed in registry on top of the priorly formed toner images. After an individual color toner images has been developed on the belt, an absorptive blotter roller biased to a potential having the same sign as the respective toner particles is used to absorb carrier fluid. The roller is porous and has a central chamber connected to a vacuum for removing liquid continuously. When a full color image has been formed on the imaging belt, it is transferred to a second belt. The full color image is then transported to come into contact with an absorptive belt for removing additional carrier fluid, after which the full color toner image is heated, thereby forming two phases including a toner-rich phase and a nearly pure carrier phase. The heated full color toner image is then transferred to a receiver under transfix conditions, i.e., without the need for an electric field. The Lewis patent (U.S. Pat. No. 5,987,284) discloses a xerographic method and apparatus for conditioning a liquid developed image. A metering roller is used to remove excess carrier liquid from a liquid developed toner image, and subsequently an electrically biased roller is used to electrostatically compress the toner image, e.g., on an imaging member or on an intermediate transfer member. The roller is porous and includes a central chamber connected to a vacuum for removing carrier liquid continuously. The Seong-soo Shin et al. patent (U.S. Pat. No. 6,085,055) discloses an external blotter roller for removing excess carrier liquid from a liquid developed electrophotographic image formed on a photoconductive belt. Liquid is thermally removed from the roller by evaporation, the roller being contacted and heated by heating rollers. The vapors are condensed to liquid which is collected.
Dispersions such as liquid developers for use in electrophotography and nonaqueous inks for use in ink jet recording have in common the use of an organic carrier fluid, typically a hydrocarbon. In particular, mixed alkanes commercially marketed by the Exxon Corporation under the trade name, Isopar, are useful. Various Isopars having different flash points and evaporation rates are available. Liquid developers made with Isopars having flash points greater than 140xc2x0 F., e.g., Isopar L and Isopar M, have been disclosed in the Santilli et al. patent (U.S. Pat. No. 5,176,980). Nonaqueous inks including Isopars are disclosed by the Nicholls patent (European Patent No. 0939794), the Nicholls at al. patent (U.S. Pat. No. 5,453,121), the Kohyama patent (U.S. Pat. No. 6,126,274) and the Kato patent (U.S. Pat. No. 6,133,341), cited above.
An imaging method and apparatus involving electrocoagulation of a primarily aqueous dispersion has been disclosed by the Castegnier et al. patents (e.g., U.S. Pat. Nos. 3,892,645, 4,555,320, 4,661,222, 4,895,629, 5,538,601, 5,609,802, 5,693,206, 5,727,462, 5,908,541 and 6,045,674) wherein an electric current is passed between a positive electrode (or an array of positive electrodes) and a negative electrode (in an array of negative electrodes) to produce an electrocoagulated deposit on the positive electrode. An imagewise electrocoagulated deposit may be transferred to a receiver such as paper to form a single color image, e.g., a black image, on the paper. Alternatively, imagewise electrocoagulated deposits of different colors may be sequentially deposited, e.g., on a positively biased belt, so as to form a full color image for subsequent transfer to a receiver. There is no disclosure for using an intermediate member in conjunction with electrocoagulation. A squeegee blade apparatus for removing excess liquid is disclosed in the Castegnier et al. patents (U.S. Pat. Nos. 5,928,486 and 6,090,257). A difficulty inherent in the electrocoagulation technique is that image uniformity requires an extremely accurate distance between each pair of opposing positive and negative electrodes, typically about 50 micrometers. Moreover, the image resolution is limited by the diameter of individually addressable electrodes and also by the fact that these electrodes must be isolated from one another by a thickness of insulating material between them. There are other difficulties, e.g. that the electrical power density required for creating an electrocoagulated image is relatively high, that special materials are needed to suppress unwanted gas generation near the electrodes, and that electrodes must be protected against electrolytic erosion. The Castegnier et al. patent (U.S. Pat. No. 4,555,320) discloses a relatively low resolution of 200 dots per inch requiring 25 watts of power (50 volts, 500 ma) to produce 100,000 developed dots per second, which is equivalent to about 100 microcoulombs of charge delivered in about 0.4 second per developed dot, resulting in a significant power density of about 4.1 watts/in2 if every imaging pixel is developed (maximum density flat field image). The Castegnier patent (U.S. Pat. No. 4,764,264) discloses a resolution of 200 dots per inch requiring 25 watts of power to produce 1,000,000 developed dots per second, each developed dot requiring passage of 25 microcoulombs of charge.
There remains a need for a simplified, non-electrostatographic method for forming high resolution color images, which simplified method does not include any electrostatic latent image, nor development of any latent image by an electroscopic toner, nor a first transfer of any developed electroscopic toner image to an intermediate transfer member for a subsequent second transfer to a receiver member. Moreover, there remains a need to improve upon the electrocoagulation imaging method as disclosed in U.S. Pat. Nos. 3,892,645, 4,555,320, 4,661,222, 4,895,629, 5,538,601, 5,609,802, 5,693,206, 5,727,462, 5,908,541 and 6,045,674 cited above, which method requires high power density and an expensive write head, has limited resolution, and has problems with electrochemical erosion of the electrodes and gas generation by the electrodes. Furthermore, there remains a need to circumvent problems associated with apparatus such as described for example in above-cited U.S. Pat. Nos. 5,992,756, 6,019,455, 6,126,274 and 6,133,341, in which a pigmented ink is concentrated in an ink jet write head so as to eject agglomerates of toner particles, the main problems including plateout of ink particles in the write head, ink replenishment and liquid flow problems in the write head, and the need for a complicated electrode configuration in an expensive writehead.
The invention provides a digital imaging method and apparatus including: an ink jet device utilizing a coagulable ink, an intermediate member upon which a primary ink jet image is formed from ink droplets produced by the ink jet device, a physical or chemical agent or a mechanism to cause a formation of coagulates in the primary ink jet image on an operational surface of the intermediate member, a mechanism for removing excess liquid from the coagulates, a transfer mechanism for transferring the liquid-depleted coagulates to a receiver member, and a regeneration device for regenerating the operational surface prior to forming a new primary image thereon. The ink includes aqueous-based and nonaqueous dispersions and single-phase solutions of a soluble coagulable colorant or a dye.
More particularly, the invention provides a digital imaging method and apparatus including: an ink jet device utilizing an ink containing dispersed pigmented particles in aqueous-based or nonaqueous colloidal dispersions, an intermediate member upon which a primary ink jet image is formed from ink droplets produced by the ink jet device, an agent or mechanism to cause physical or chemical aggregation of the pigmented particles into flocs, coagulates or agglomerates so as to form an aggregated ink jet image on the intermediate member, a mechanism for removing excess liquid from the flocculated, coagulated or agglomerated pigmented particles so as to form a liquid-depleted image from the primary image, a transfer mechanism for transferring the aggregated pigmented particles of the liquid-depleted image to a receiver member, and a regeneration device for removing from the operational surface residual material remaining on the operational surface after the transferring of the liquid-depleted image to the receiver.
In one aspect of the invention, the ink jet ink is an aqueous-based dispersion of pigmented particles. In one embodiment, the aggregation of the particles in the primary ink jet image is produced by a heating or a cooling of the primary image on the intermediate member. In other embodiments, the aggregation of the particles in the primary ink jet image is produced by an added salt dissolved in the liquid of the primary image. In yet other embodiments, the aggregation of the particles in the primary ink jet image is produced by altering the pH of the liquid of the primary image. In further embodiments, the aqueous-based ink has a steric stabilization produced by polymeric moieties adsorbed on the surfaces of the pigmented particles, and the aggregation of the particles in the primary ink jet image is induced by causing a desorption, or decomposition, of the sterically stabilizing moieties. In still further embodiments, the aggregation of the particles in the primary ink jet image is produced by an electrocoagulation using an electrode external to the intermediate member. In yet another embodiment, a sterically stabilized nonaqueous primary ink jet image is destabilized by adding dissolved polymeric molecules which are soluble in (compatible with) the aqueous-based carrier liquid. In still yet another embodiment, a hetero-colloid is added to the primary image to form hetero-coagulates.
In another aspect of the invention, the ink jet ink is a nonaqueous dispersion of pigmented particles. In one embodiment, the aggregation of the particles in the primary ink jet image is produced by a heating or a cooling of the primary image on the intermediate member. In other embodiments the nonaqueous ink has a steric stabilization produced by polymeric moieties adsorbed on the surfaces of the pigmented particles, which moieties having chains extending into and soluble in the carrier fluid of the ink jet ink dispersion, and the aggregation of the particles in the primary ink jet image is induced by a destabilizing liquid or solvent that comes into contact with and mixes miscibly with the liquid of the primary image, the polymeric chains of the moieties being insoluble in the destabilizing liquid. In further embodiments, the nonaqueous ink has a steric stabilization produced by polymeric moieties adsorbed on the surfaces of the pigmented particles, and the aggregation of the particles in the primary ink jet image is induced by causing a desorption, or a decomposition, of the sterically stabilizing moieties. In yet a further embodiment, a sterically stabilized nonaqueous primary ink jet image is destabilized by adding dissolved polymeric molecules which are soluble in (compatible with) the nonaqueous carrier liquid of the primary ink jet image.
In certain embodiments of the invention in which the ink is a nonaqueous dispersion, the liquid removal mechanism to form a concentrated image is similar to any known mechanism for removing a carrier liquid from a liquid-developed toner image situated on an electrostatographic primary imaging member or on an electrostatographic intermediate transfer member.